It is known in the art of downhole probe design to employ covers or coatings to protect the external probe surfaces from undue wear, as abrasive liquid/solid mixtures are often transported in the pipeline or conduit that houses the probe. The covers may be manufactured separately and installed on the external surface of the probe, or they may be in the form of a spray-coating or similar application technique. The cover or sleeve material is commonly in the form of a plastic or metal material, the specific material selected on the basis of the application and the type, volume and velocity of fluid flow around the probe.
For example, U.S. Pat. No. 7,114,562 to Fisseler et al. teaches a measurement-while-drilling apparatus and method wherein the probe is provided with a releasably secured protective cover to protect the probe during drilling.
The use of a plastic sleeve is also known to have potential advantages in the field of downhole electromagnetic telemetry, as commonly-used gap subs employ some degree of electrical isolation for operation. As is taught in Patent Cooperation Treaty Application No. PCT/CA2013/050850 to Logan et al., an electrically insulative coating or sleeve can be used with a gap sub probe.
However, it is known that sleeves can be dislodged by normal fluid flow through a conduit, particularly in the context of drilling fluids or other high-velocity applications, as the fluids can flow beneath the leading or upstream edge of the sleeve and damage it and/or pull it away from the probe external surface, allowing abrasive fluids to damage the probe itself.
Some solutions have been proposed, such as using an adhesive to retain the sleeve against the external probe surfaces, but this makes it more difficult to remove the sleeve. In the situation where the sleeve is sacrificial and is intended to be replaced from time to time, having the sleeve glued in place renders such replacements difficult. Additional time and cost may be required to remove such adhered sleeves, with the potential for damaging the probe itself.
What is needed, therefore, is a means for providing a sacrificial sleeve for the external surface of a probe or other in-conduit device, while securing at least the upstream end of the sleeve to prevent or reduce the risk of fluid getting beneath the sleeve. Preferably, such means would not include the use of adhesives and would allow for easier replacement of worn sleeves.